Population dynamics, growth and energetics of jellYfish Aurelia aurita in a shallow fjord

Seasonal abundance and growth of the scyphomedusa Aurelia aunta were studied during 1991 and 1992 In the Inner part of a small shallow fiord, Kertinge Nor, Denmark Uunng both years, mass occurrence of A aunta was observed, and a maximum value of ca 300 ind m-3 was measured In Apnl 1992 Growth was poor in the fiord and the maximum mean umblella diameter of medusae was only 54 i 12 mm and 37 + 15 mm In 1991 and 1992 respectively Growth, clearance, lngestlon and resplratlon were measured at different prey concentrations in the laboratory, and an energy budget was estabhshed Ephyrae (4 mm in diameter] were offered rotiferas (Brachjonus plicatllls) in concentrations ranging from 7 to 13000 ind I ' Clearance of ephyrae decreased 30 to 5 0 % with increasing prey concentration, and a curved relationship between prey concentration and lngestlon was found A maximum speclflc growth rate of 0 2 d ' was measured In the laboratory at 400 B plicatilis 1 ', correspondlng to 60 pg C 1. ' In Kertinge Nor, the growth rate never exceeded 0 1 d ' The average zooplankton concentration In Kertinge Nor was only 5 p g C I ' and it could therefore be concluded that A aunta was food hmited in the fiord